Max Hillebrand on Nostr: The SHA-256 algorithm processes input data to produce a 256-bit hash value. Here's a ...

The SHA-256 algorithm processes input data to produce a 256-bit hash value. Here's a step-by-step walkthrough of the algorithm:

1. Padding: The input message is padded to make its length a multiple of 512 bits. This is done by appending a single '1' bit, followed by '0' bits, and then a 64-bit representation of the original message length.

2. Initialization: Eight 32-bit buffers (A to H) are initialized with specific hexadecimal values derived from the first 32 bits of the fractional parts of the square roots of the first 8 prime numbers.

3. Message schedule: The padded message is divided into 512-bit blocks. Each block is further divided into 16 32-bit words. These words are expanded into 64 32-bit words using a specific formula.

4. Compression function: This is the core of the algorithm, consisting of 64 rounds of operations. In each round:
The current state (A to H) is mixed with the message schedule word and a constant K[i].
Bitwise operations (AND, XOR, rotations) are performed.
The state is updated for the next round.

5. Final addition: After processing all blocks, the final values of A to H are added to their initial values.
Output: The final state of the eight 32-bit words (A to H) is concatenated to produce the 256-bit hash value.

This process ensures that any change in the input, no matter how small, results in a completely different hash value, making SHA-256 useful for integrity verification and digital signatures.